This invention relates to a method of producing a lubricant for a magnetic disk, a lubricant for a magnetic disk, a magnetic disk, and a method of producing a magnetic disk. More particularly, this invention relates to a method of producing a lubricant which provides a magnetic disk suitable for a load unload system and having a lubrication layer capable of suppressing a fly stiction defect or a contamination on a surface of a magnetic head even if the magnetic head has a very narrow flying height of 12 nm or less, a lubricant obtained by the method, a magnetic disk obtained by using the lubricant and having the above-mentioned feature, and a method of producing the magnetic disk.
In a magnetic disk apparatus such as a hard disk drive (HDD), a CSS (Contact Start Stop) system has been used. In the CSS system, when the magnetic disk apparatus is stopped, a magnetic head is kept in contact with a contact-start-stop region (CSS region) formed in an inner peripheral region on a surface of a magnetic disk. In a starting operation, the magnetic head slides on the CSS region in contact therewith to be slightly floated up. Thereafter, a recording or a reproducing operation is carried out on a recording/reproducing region formed outside the CSS region. In a stopping operation, the magnetic head is retreated from the recording/reproducing region to the CSS region and stopped after landing and sliding on the CSS region in contact therewith. The starting operation and the stopping operation in which contact sliding movement occurs will collectively be called a CSS operation.
In a magnetic disk for the CSS system mentioned above, it is necessary to form both the CSS region and the recording/reproducing region on the surface of the magnetic disk. Further, in order to prevent stiction between the magnetic head and the magnetic disk when the magnetic head and the magnetic disk are contacted, it is necessary to provide the surface of the magnetic disk with a texture having a predetermined surface roughness. In order to suppress a damage due to the contact sliding movement between the magnetic head and the magnetic disk during the CSS operation, proposal is made of a magnetic disk medium coated with a perfluoroalkylpolyether lubricant having a structure of HOCH2—CF2O—(C2F4O)p—(CF2O)q—CH2OH (for example, see Japanese Unexamined Patent Application Publication (JP-A) No. S62-66417). Proposal is also made of a lubricant for a hard magnetic disk, which contains a specific phosphazene compound as a main component (for example, see Japanese Unexamined Patent Application Publication (JP-A) No. H11-224419).
Recently, a magnetic disk apparatus of a load unload system is being introduced instead of the above-mentioned CSS system. Hereinafter, the load unload system may appropriately be called a LUL system. In the LUL system, when the magnetic disk apparatus is stopped, a magnetic head is retreated to a tilting table, called a ramp, which is positioned outside the magnetic disk. In a starting operation, the magnetic head slides from the ramp onto the magnetic disk after start of rotation of the magnetic disk. Thereafter, a recording or reproducing operation is carried out. A series of the above-mentioned operations are collectively called an LUL operation. As compared with the CSS system, the LUL system assures a wide recording/reproducing region on the surface of the magnetic disk and is therefore preferable in view of an increase in information capacity. Further, in the LUL system, the texture required for the CSS system need not be formed on the surface of the magnetic disk so that the surface of the magnetic disk can be extremely flattened and smoothed. Accordingly, the flying height of the magnetic head is significantly reduced so that a recording signal is increased in S/N ratio. Thus, the LUL system is advantageous.
Following the introduction of the LUL system, the flying height of the magnetic head is significantly reduced as mentioned above. Under the circumstances, it is required for the magnetic disk to stably operate even if the magnetic head has a very low flying height of 12 nm or less. However, when the magnetic head flies and runs on the surface of the magnetic disk at such a very low flying height, a fly stiction defect and a head corrosion defect are frequently caused to occur.
The fly stiction defect is a defect that the magnetic head is fluctuated in flying position or flying height during flying and running. The fly stiction defect is accompanied with irregular fluctuation in reproduction output. In the worst case, the magnetic disk is contacted with the magnetic head during flying and running to cause a head crash defect, resulting in breakage of the magnetic disk.
On the other hand, the corrosion defect is a defect that a device portion of the magnetic head is corroded to cause a trouble in the recording or the reproducing operation. Sometimes, the recording or the reproducing operation becomes impossible or a corroded device is expanded to damage the surface of the magnetic disk during flying and running.
Recently, in order to increase a response speed of the magnetic disk apparatus, the rotation speed of the magnetic disk is increased. In a 2.5-inch magnetic disk apparatus as a small-sized magnetic disk apparatus suitable for mobile applications, the rotation speed has been about 4200 rpm in the past. Recently, the magnetic disk is rotated at a high rotation speed of 5400 rpm or more to thereby improve a response characteristic. Such high-speed rotation of the magnetic disk exposes a phenomenon that a centrifugal force following the rotation causes migration of a lubrication layer and, consequently, the thickness of the lubrication layer becomes nonuniform in a plane of the magnetic disk. If the thickness of the lubrication layer is increased at an outer periphery of the magnetic disk, the fly stiction defect or the head crash defect is easily caused to occur during the LUL operation. If the thickness of the lubrication layer is decreased at an inner periphery of the magnetic disk, a lubricating performance is decreased so that the head crash defect is easily caused to occur.
With the conventional lubricants described in the above-mentioned publications, these defects are frequently caused to occur. It is therefore difficult to satisfy a reliability required for recent magnetic disks. Thus, the magnetic disk is inhibited from an increase in capacity, an improvement in S/N ratio, and an increase in response speed.